Occupational exposure to chemicals and cancer

Abstract

We spend a lot of our time at work and the exposures in our work environment have a great influence on our health. Certain occupational groups, like firefighters, are exposed to a large number of chemicals and an increased risk of cancer has been reported in this group. Also, the association between certain chemicals and cancer types have been studied, like organic solvents and breast cancer. However, there is still a need for better understanding on chemicals’ possible effect on the cancer risk. The aim of this thesis was therefore to investigate the association between occupational exposure to chemicals and the risk of cancer, focusing on breast cancer, women’s most common form of cancer, and firefighters, a male-dominated occupation where workers are exposed to a large number of chemicals.

Data for this thesis were derived from Malmö Diet and Cancer study (MDCS) and a cohort of firefighters in Stockholm. Papers I, II and III are based on MDCS and paper IV is based on the firefighter cohort. MDCS is a prospective cohort study following 17 035 women born 1923-1950 and living in Malmö during the recruitment years 1991-1996. Diagnoses of breast cancer were identified through the Swedish Cancer registry from inclusion to 2013. Occupational history (three latest occupations) was self-reported at baseline and two different job-exposure matrices were used to estimate the chemical exposure. For paper III an occupational hygienist made a case-by-case exposure assessment based on additional occupation data in the questionnaire. For paper IV a cohort of 1080 men working as firefighters in Stockholm for at least one year between 1931-1983 were followed from 1958-2012 for cancer diagnoses.

Paper I showed that white-collar workers had an increased risk of breast cancer, even after adjusting for risk factors related to lifestyle and reproduction. Papers II and III showed that women exposed to chemicals in their occupational environment had an increased risk of breast cancer that appeared to be correlated with duration of exposure. Specifically in paper III, women exposed to chlorinated hydrocarbon solvents and oil mist had an increased risk of breast cancer. Paper IV showed an overall low risk for cancer among firefighters. However, an increased risk for stomach cancer was found that could possibly be related to their occupational exposures.

This thesis gives some support to the hypothesis that organic solvents are associated with breast cancer. It also indicates that the exposure limit for oil mist might need revision by the Swedish Work Environment Authority since results show that women exposed under the set limit have an increased risk of breast cancer. Our results suggest that the exposure assessment using a JEM in combination with a case-by-case estimation by an occupational hygienist gave an improved risk estimate, compared to only using a JEM.